Production of permanent magnets and alloys therefor



Patented Mar. 7, 1950 9 PRODUCTION OF PERMANENT MAGNETS AND ALLOYS THEREFOR John R. Hansen, Summit, N. J assignor to Crucible Steel Company of America, New York, N. Y., a corporation of New Jersey No Drawing. Application October 3, 1946,

Serial No. 701,053

9 Claims. (Cl. 75-424) This invention pertains to improvements in ferrous alloys containing aluminum, nickel and cobalt, and optionally also copper, adapted primarily for use in permanent magnets, to permanent magnets thereof, and to processes for producing the same.

It is known to make permanent magnets of an alloy containing from about 6 to 11% aluminum, 12 to nickel, 16 to cobalt, up to about 7% copper, and the balance substantially iron, socalled alnico alloys. It is also known to enhance the magnetic properties of such'magnets, particularly the (Bl-I) max values, by rendering the same magnetically anisotropic by heat treatment, i. e. by cooling from above to well below the Curie point while in a magnetic field the lines of force of which follow the direction of subsequent permanent magnetization of the magnets.

However, a serious drawback to the attainment of optimum magnetic properties with magnets of the above alloy analysis, is the susceptibility of the alloy to the formation of a multi-phase, usually a two-phase, microstructure, whereas best permanent magnet properties are secured with a single-phase microstructure.

With reference to this point, the microstructure of an alloy of the above analysis is found to be efiected by heat treatment as follows: After homogenizing or normalizing at about 2300 to 2400 F., the alloy will be found to embody a single-phase microstructure. This phase has been identified as having the alpha body centered cubic structure, and is accordingly referred to' herein as the alpha" phase. However, on heating the alloy at about 1500 to 1600 F., the precipitation of a new phase, designated herein as the beta phase, occurs, whereby the alloy assumes a twophase microstructure comprising the solid solution or alpha phase having the beta phase dispersed therein in a fine state of subdivision. This beta phase appears to comprise a precipitate of intermetallic compounds derived from the various alloying constituents. This two-phase microstructure consisting of the alpha and beta phases is also observed in the alloy in the as-cast" condition. On heating the alloy to a slightly higher temperature of about 1650 F., a single-phase microstructure, consisting only of the alpha phase, is obtained. At higher temperatures, however, of about 1700 to 2250 F., the precipitation of a third phase occurs, referred to herein as the gamma phase, which results on cooling from this temperature range, in a two-phase microstructure comprising a mixture, in varying proportions, of the alpha and gamma phases.

The gamma phase is so designated because there are indications that it consists of gamma iron at the above stated elevated temperature and undergoes transformation to a martensitic-like constituent, as observed under the microscope, on cooling to room temperature.

Both of the two-phase microstructures aforesaid have distinctly inferior magnetic qualities as compared to the single -phase'structure resulting from heat treating thealloy at 1650 F. or at 2300 to 2400" F. as aforesaid. This is shownjby the test data set forth in Table I below,-accordging to which individual testbars made of analloy of the above character and having'the chemical analysis given in the table, were first soaked respectively at'the progressively increasing tear peratures given in column 1, were thereupon cooled in a magnetic field tobelow the Curie point and down to a temperature of about 950 to 1000" F., and thereupon drawn or tempered for five hours at l F. Column 2 shows the relative flux values for the individual specimens resulting from the treatment aforesaid; while column 3 shows the resulting microstructures thereof.

- TABLE I Chemical Analysis of Specimen Tested, Percent Alloy 0 Mn Si Al Ni Co Cu Fe A .02 .03 .02 a 7 14. .s 24. 7 ga a Bel.

- Column 2 Re- Column 1, Column 3,

Heat Treat- Resul ing ment l'fl einp Cooling Miigrfi e v-uc.

' nctlc Field 1, 600 75. 0 11+!) 1,650 100. 0 a l, 700 92. 3 0+ 2% g l, 800 51.5 a+l0% 7 1,900 44. 9 a+25% a 2, 000 29. 5 a+35% a 2,100 38.5 a+25% g 2,200 65. 3 a+l5% a 2, 300 100. 0 a 2, 370 100.0 a

Nomenclatprez a, b and g designate the alpha, beta and gamma phases respectively.

treatments resulting in the single-phase microstructure as indicated in the table. For heat resulting in the two-phase microstructures, either that embodying the alpha plus beta phases, or that embodying the beta plus gamma phases, the flux values obtainable are materially less than those obtainable for the single-phase microstructure comprising only the alpha phase. It will also be noted that in the two-phase structure containing the gamma phase, the magnetic properties progressively decrease with increase in percentage of the gamma constituent.

The test results of Table I would appear to indicate that, for purposes of imparting the desired single-phase microstructure to as-cast permanent magnets of the above-mentioned alloy, and also for imparting the desired anisotropic magnetic qualities thereto, it would sufiice to heat the magnets to a temperature of about 1650 F. followed by cooling substantially below the Curie point in a magnetic field. I have found, however, that in the quantity production of such magnets on a commercial scale, this is decidedly not the case, due for example to such factors as: the tendency of the two-phase microstructure of the ascast magnet to persist on reheating, the strong gamma-phase forming tendencies of carbon unavoidably present in the alloy, and also to variations in individual melts due to melting tolerances, whereby such gamma-phase forming constituents as nickel and cobalt may be present in disproportionate amounts in individual melts, etc.

Due to such considerations, I have found it to be necessary with Alnico alloys of the above mentioned analysis, first to subject the magnets thereof to a normalizing heat treatment within precisely regulated temperature limits, and thereafter to reheat within precisely regulated lower temperature limits prior to cooling in the magnetic field for imparting the above-mentioned single-phase microstructure and anisotropic magnetic qualities to the magnets. Thus, the alloy, after casting into a magnet and subjecting to preliminary processing operations, such as grinding, etc., must be given an initial or normalizing heat treatment, consisting in homogenizing at 2350 to 2400 F. for about fifteen minutes, followed by a rapid cool to room temperature. For imparting the above-mentioned anisotropic properties to the magnet, it must then be reheated above the Curie point (i. e., the temperature at which the alloy transforms from magnetic to nonmagnetic), and within the very restricted and critical temperature range of 1610 to 1660" F., for about five to sixty minutes until thoroughly soaked at temperature, this to assure substantial retention of the single-phase microstructure on subsequent cooling. Thereupon, the magnet is cooled in a magnetic field, as aforesaid, until it is sufficiently below the Curie point to secure the full anisotropic effect of the magnetic field, this cooling being ordinarily carried down to a temperature within the range of about 1000 to 1200 F. The magnet is thereupon removed from the magnetic field and air-cooled to room temperature. It is then reheated or drawn at a temperature somewhat above 1100 F. and then cooled below 950 for purposes of further improving its magnetic qualities.

The above contrasts with the normal heat treatment to which magnets of this character have been subjected in accordance with prior practices. The normal heat treatment for the designated Alnico alloys consists in normalizing or homogenizing at the temperatures from 2300 to 2425 F. This is followed by controlled cooling in a magnetic field to substantially below the Curie point, after which the magnet castings are then subjected to a draw operation which consists of reheating to within the temperature range of 950 to 1250 F. for a period of time dependent on the particular temperature or temperatures being employed. The magnets are then cooled to room temperature.

I have found that for reasons above stated, the aforementioned normal heat treatment is inadequate in that it does not impart optimum magnetic properties to the magnets when massproduced on a commercial scale, due to the precipitation of the designated gamma phase on cooling. This undesirable condition has been traced to the heat chemistry wherein unfavorable balance exists between the various alloying elements even though said alloying elements are within the tolerance limits of the manufacturing specification. This precipitation is also found to occur on cooling magnet castings of relatively large section, even when possessing a favorable balance of alloying elements. This is due to the greatly retarded cooling rate imparted to the mass involved.

Now I have further discovered, in accordance with the principal aspect of the present invention, that by the addition of small but substantial amounts of silicon to the alloy having the abovementioned range of analysis, the desired singlephase microstructure aforesaid may be retained on cooling the alloy from much broader temperature ranges than those aforesaid, and that, in consequence, the heat treatment of magnets made of the aforesaid Alnico alloy incorporating silicon in accordance with my invention, may be greatly simplified. Thus, I find that by adding silicon to the aforesaid alloy in the amount of about 0.15 to 1%, and preferably in the amount of about 0.2 to 0.4%, by weight of the resulting alloy, the initial normalizing heat treatment, consisting in homogenizing at 2350 to 2400" F. and quenching therefrom which I have found to be otherwise required, may be entirely eliminated; and that, furthermore, the heating of the magnet above the Curie point, for imparting the anisotropic properties referred to, may be carried out within a much broader temperature range, viz., 1590 to 1700 F., than the narrow and critical temperature range of 1610 to 1660 F. which I have found to be required with the alloy omitting the silicon content.

The permanent magnet alloy in accordance with my invention has the following broad and preferred ranges of analysis:

Carbon-as low as possible, i. e. 0 to 0.1% max.,

and preferably under 0.05% max.

Manganese0 to 1% Nickel-10 to 20% Cobalt16 to 30% Aluminum-6 to 11% Copper0 to 7% and preferably 0 to 3.5%

Silicon-0.15 to 1%, and. preferably 0.2 to 0.4%

Remainder-substantially iron.

I find that in addition to the advantages above stated resulting from the use in permanent magnets of my improved alloy containing silicon, permanent magnets thereof have materially better average and optimum magnetic properties than similar magnets made of the alloy excluding silicon. Thus, in the commercial or quantity production of permanent magnets made of my alloy, I find that the (BIDmax values thereof range consistently above 4.5 million and up to 5.5 million or higher, as compared to corresponding values ranging from about 4 to 5 million obtained in the quantity production of similar magnets made of the alloy omitting silicon. Stated somewhat differently, by employing the alloy of my invention in the quantity production of permanent magnets, a minimum (BH)max of 4.5 million is assured, whereas this value is frequently as low as 4.0 million for magnets made of the alloy omitting silicon.

In Table II below, I give the results of comparative tests typifying the improvements in magnetic properties of permanent magnets resulting from silicon additions, in accordance with my invention, to the aforesaid previously known alloy omitting silicon. In accordance with these tests, heats were made of alloys having the chemical analyses set forth in Table II as alloys A to C respectively, these alloys analyzing substantially the same except for silicon which was present therein in the percentages of 0.02, 0.26 and 0.61 respectively, as indicated. For the magnetic tests, fl -inch square bars of each analysis were made up and ground to T e inch square, cut to 2-inch lengths and squared on the ends to 1.875 inch in length. These were normalized in a gas-fired rotary furnace at 1650 F. for fifteen to twenty minutes, and thereupon cooled to 1100 F. in 4.5 minutes, while in a magnetic field. The specimens were then drawn by heating to 1125 F. for five minutes and furnace-cooled to 950 F. in sixty minutes, and checked for magnetic properties in the permeameter with the results as given in Table II.

TABLE II Chemical Analysis of Specimens Tested, Percent Alloy C Mn Si Al Ni Cu Bal.

A .020 03 .02 8. 7 l4. 5 24. 7 3. 3 Fe B .015 .02 .26 8.7 13.5 23.9 3.1 Fe O .015 .02 .61 8. 4 13.4 23.7 3.1 Fe

Results of Magnetic Tests Alloy A Alloy B Alloy C .02% Si 26% Si .61% Si He 510 572 502 Br 12, 650 12, 860 13, 180 Ed 495 430 Ed 10, 000 10, 800 (8K), 4. 22 4. 95 4. 65

It will thus be seen that the addition of silicon within the limits above stated has greatly increased the (BH)max value without sacrifice in other magnetic qualities, the increase amounting to about 20% for the 26% silicon addition.

Table III below gives the results of comparative tests on alloys A to C respectively of Table II, to show the effects of silicon additions in restricting the formation of a two-phase microstructure, on cooling the alloys to progressively lower temperatures from the normalizing temperature before quenching; while Table IV below shows, for the same alloys, the efiects of silicon additions in restricting the formation of a twophase microstructure, on heating the alloy from room temperature to progressively increasing temperatures.

TABLE III [Nomenclaturen a-alpha phase, g-gamma ph ase.]

0 Alloy A Alloy B Alloy 0 Heat Treatment, F. 02% Si 26% Si 61% Si 240015' cooled to:

2400Water Quench.... a 2300-l0 Water Quench. a. u. 2250-l0 Water Quench. a. a. 220010 Water Quench.. a. a 2l50l0 Water Quencln. a a. 2100-10 Water Quench. a+35% 9-- a a. 2050l0 Water Quench. a+35% g.- a-I-trace g. a. 2000-l0 Water Quench. a+35% 9.- a+5% g. a+trace g. l950l0 Water Quench.. a+35% 9.- a+25% g. a+trace 11.

TABLE IV [Nomenclaturez aalpha phase, ggamma phase] 0 Alloy A Alloy B Alloy 0 Heat Treatment, F. 02% Si 26% Si Si l700-30 Air Cool a+l% g a. l75030 Air (3001-- a+l% g a+l% 9.- a. 1R0030 Air 0001. a-ll0% g a+l% ga+l% g l85030 Air Cool. a+10% g a+l0% 0.- a+l% g l90030 Air Cool. a+l0% a. a+30% g (kl-1% g l95030 A r 0001.. a+30% g a+25% 9-- a+5% g l70060 Air Cool a+35% g a a.

It will be observed from Tables III and IV that the effect of silicon is greatly to restrict the formation of the two-phase microstructure, both as regards cooling from the normalizing temperature and as regards heating from room to elevated temperature. Thus, as shown by Table III, where silicon is present in the alloy in the amounts stated, the single phase microstructure is obtained on normalizing or homogenizing over the relatively wide temperature range of 2100 to 2425 F. Tests of a similar nature have established that where silicon is present in the amounts stated, the single phase microstructure is also obtainable by the single step of heating the as-cast magnet within the relatively broad lower temperature range of about 1590 to 1700 F.

It is by reason of these effects that I am enabled in the quantity production of silicon containing permanent magnets in accordance with my invention to obtain the desired single phase microstructure, either by the single step normalizing or homogenizing the as-cast magnet over the relatively broad temperaturerange of 2100 to 2425 F., or alternatively, by the single step of heat treating the as-cast magnet within the lower temperature range of 1590 to 1700 F. The first procedure above-mentioned, viz., normalizing or homogenizing to 2l00 to 2425 F., constitutes a modification of the normal heat treatment above described, and one which results in a satisfactory magnet. My preferred heat treatment, however, is that last mentioned, namely, the complete omission of the normalizing treatment previously required, and the substitution therefor of the single step of heat treating within the temperature range of about 1590 to 1700" F.

Thus the production and preferred heat treatment of the magnets, in accordance with my invention, are as follows: The magnet is cast and subjected to the usual preliminary processing operations, such as grinding, etc. It is then heat treated by heating above the Curie point, and held above this point for about five to sixty minutes until thoroughly soaked at temperature. Ordinarily, this heating is carried out at about 1590" to 1700 F. The magnet is then transferred to a magnetic field of about 600 to 3000 gauss and air-cooled sufliciently below the Curie point to secure the full anisotropic effect of the magnetic field, this cooling being ordinarily carried down to a temperature within the range of about 1000 to 1200 F. The magnet is then removed from the magnetic field, and air-cooled to room temperature. It is thereupon reheated above 1100 F. and cooled therefrom at about 25 to 50 per hour, either slowly or in successive steps, down to a temperature of about 950 F., and thereupon aircooled to room temperature. A magnet made of the silicon-containing alloy of my invention, and heat treated as aforesaid, will have a (BH) max ranging consistently above 4.5 million and up to 5.5 million or more.

In order further to demonstrate the effectiveness of silicon additions to Alnico alloys of the type aforementioned, permeameter values are given in Table V below, of two magnets possessing the relatively large sectional dimensions and the chemical analysis given in said table. The permeameter values were obtained on sections cut from magnets having minimum slip coil values. The magnet castings were heat treated at 1635 F. for 50 to 60 minutes, and were then cooled in a magnetic field to temperature of 1000 to 1100 F. in 9 to 11 minutes, and then removed from the magnetic field and cooled to room temperature. They were then drawn by reheating to a temperature somewhat above 1100 F. followed by cooling to about 950 F., with results as given in said Table V as follows:

In an alloy of the above type Without silicon and of corresponding sectional dimensions, optimum magnetic properties cannot be realized on heat treating from the aforesaid restricted low temperature range of 1610 to 1660 F., due to the segregation present in the as-cast condition which is imparted by the precipitation of the socalled gamma phase during the cooling after solidification. Neither can optimum properties be realized on cooling from above the gamma region within the aforesaid restricted temperature range of 2200 to 2425 F. and in a magnetic field, as reprecipitation of the gamma phase occurs. It is further not possible to cool the magnet casting rapidly from a temperature of 2200 to 2425 F. and to below the gamma region with the purpose of preventing its reprecipltation and to be followed by heat treating in a magnetic field from within the range of 1610 to 1660 F. This is due to the excessive cracking which thereby occurs.

By way of demonstrating the improvements resulting from the invention in the quantity production of permanent magnets on a commercial scale, 300-pound induction heats of the above alloy were made, directed to similar analyses except for silicon, with respect to which, however, the aim was to produce heats having silicon contents of 0.1, 0.2 and 0.3% respectively. The

TABLE VI Chemical Analyses of Magnets Tested, Percent Alloy O Si Mn Ni Cu A1 C0 Fe E. .022 .13 .02 13.65 3.20 8.36 24.00 Bal. F. .031 .23 .02 13.80 3.24 8.41 23.80 Bel. G. .015 '32 .02 13.75 3.20 8.40 24.14 Ba].

Results of permeameter tests expressed in, cumulative percentage of magnets tested having indicated (BHMMX values Alloy 1" Alloy G Si 23% Si .32% Sl Under 4.0(] 6. 25 0 0 Under 4.25. 0 0 Under 450. .95 0 Under 4.75 1.90 4. 25 Under 5.00 6.66 19. 75 Under 5.25 89. 62. 76 70. 15 Under 5.50 100. 00 100. 00 100. 00

Total Number of Magnets Tested It will be seen from the above tabulations that for the lowest silicon content of .13%, the cumulative percentage of magnets tested having (BH)max values below any given value between 4.0 and 5.5 million is considerably higher than are the corresponding percentages for the magnets having hgher silicon contents within the range of analysis of my invention. This is of importance in the rejection of magnets for low (BH) max values in quantity production. Thus, for example, if the lower acceptable commercial limit for (BI-I) max is set at 4.5 million, the above table shows that the rejections in the case of the 0.13% silicon analysis would be 12.50%, as compared to rejection of only about. 1% for the 23% silicon analysis and 0% for the .32% silicon analysis.

A direct comparison is given in the following Table VII of magnets obtained from two 300 pound production heats, in one case consisting of an alloy without silicon, and the other with silicon. The alloys are designated as H and I respectively. Alloy H was heat treated from above the gamma region; cooled rapidly to below said region and then subjected to a magnetic treatment from 1650" F. Alloy I was heat treated directly from 1650 F. into a magnetic field. Both were followed by a draw treatment which consisted of heating to somewhat above 1100 F. and cooling to about 950 F. The energy product distribution is expressed in cumulative percentages.

TABLE VII Chemical Analyses of Magnets Tested, Percent Alloy C Si Ni Cu Al Co Fe 13.90 3.36 8. 58 23. 72 B111. .28 13.90 3.22 8.44 23. 72 Ba].

9 TABLE VII-Continued Results of (BH)mnx tests expressed in cumulative percentage of magnets tested Alloy H Alloy I (BEMXW 02% Si 28% Si Under 4.75 45. 2 2. Under 5.00. 75. 2 5. 0 Under 5.25 98.3 49.1 Under 5.50.. 100 0 96.] Under 5.75 100. 0 100. 0

Total number of Magnets Tested Complete permeameter tests Alloy 11c Br (BlEUmHXlO From the foregoing table it is obvious that improved magnetic properties are obtained with the silicon alloy which are over and above those obtained when heat treating an alloy without silicon by the best known practice.

I claim:

1. A ferrous alloy adapted for use in permanent magnets containing: about to 20% nickel, about 16 to 30% cobalt, about 6 to 11% aluminum, up to about 7% copper, up to about 1% manganese, up to about 0.1% carbon, from about 0.15 to 1% silicon, and the balance substantially all iron, said silicon being present in amount such as to impart to said alloy a substantially single phase microstructure on heating at about 1600 to 1700 F. and cooling therefrom.

2. A permanent magnet made of a ferrous alloy containing: about 10 to 20% nickel, about 16 to 30 cobalt, about 6 to 11% aluminum, up to about 7% copper, up to about 1% manganese, up to about 0.1% carbon, from about 0.15 to 1% silicon, and the balance substantially all iron, said magnet having a substantially single-phase microstructure.

3. A permanent magnet made of a ferrous alloy containing: about 10 to 20% nickel, about 16 to 30% cobalt, about 6 to 11 aluminum, up to about 7% copper, up to about 1% manganese, up to about 0.1% carbon, from about 0.15 to 1% silicon, and the balance substantially all iron, said magnet having a substantially single-phase microstructure, being magnetically anisotropic and having a (BHhmX value in the principal direction of at least 4.5 million.

4. In the manufacture of permanent magnets, the process which comprises: casting into the shape of a permanent magnet a ferrous alloy containing about 10 to 20% nickel, about 16 to 30% cobalt, about 6 to 11% aluminum, up to about 7% copper, up to about 1% manganese, up to about 0.1% carbon, from about 0.15 to 1% silicon, and the balance substantially iron; thereafter heating the so-cast magnet to a temperature within the range of about 1590 to 1700 F. and allowing said magnet to cool from said temperature while in a magnetic field to a temperature sufficiently below the Curie point to impart anisotropic properties to said magnet.

5. In the manufacture of permanent magnets, the process which comprises: casting into the shape of a permanent magnet a ferrous alloy containing about 10 to 20% nickel, about 16 to 30% cobalt, about 6 to 11% aluminum, up to about 3% copper, up to about 0.1% carbon, from about 0.2 to 0.4% silicon, up to about 1% manganese, and the balance substantially iron; thereafter heating the so-cast magnet to a temperature within the range of about 1590 to 1700 F. and allowing said magnet to cool from said temperature while in a magnetic field to a temperature sufficiently below the Curie point to impart anisotropic properties to said magnet.

6. In the production of permanent magnets,

the process which comprises: casting into the form of a magnet a molten ferrous alloy containing about 10 to 20% nickel, about 16 to 30% cobalt, about 6 to 11% aluminum, up to about 3% copper, up to about 0.1% carbon, from about 0.2 to 0.4% silicon, up to about 1% manganese, and the balance substantially iron; allowing the so-cast magnet to cool substantially to room temperature; thereupon heating the magnet to a temperature within the range of about 1590 to 1700 F. until thoroughly soaked at said temperature; applying to the so-heated magnet a magnetic field, said field being applied in the direction of permanent magnetization of said magnet; allowing the magnet to cool in said field to a temperature sufficiently below the Curie point to render said magnet magnetically anisotropic; and thereupon heating said magnet above 1100 F. and allowing it to cool below 950 F.

7. The method of heat treating a permanent magnet containing about 10 to 20% nickel, about 16 to 30% cobalt, about 6 to 11% aluminum, up to about 7% copper, up to about 1% manganese, up to about 0.1% carbon, and the balance principally iron, said method comprising: heating said magnet to temperature of about 2350 to 2400 F. and thereupon cooling substantially to room temperature, thereupon reheating the magnet to temperature of about 1610 to 1660 F. until thoroughly soaked at temperature, and cooling in a magnetic field to a temperature sufficiently below the Curie point to impart anisotropic properties thereto.

8. A ferrous alloy adapted for use in permanent magnets, containing: about 10 to 20% nickel, from more than 20% to about 30% cobalt, about 6 to 11% aluminum, up to about 7% copper, up to about 1% manganese, up to about 0.1% carbon, from about 0.15 to 1% silicon, and the balance substantially all iron, said silicon being present in amount such as to impart a substantially single phase microstructure to said alloy upon heating at about 1600 to 1700 F. and cooling therefrom.

9. A permanent magnet made of a ferrous alloy containing: about 10 to 20% nickel, from more than 20% to about 30% cobalt, about 6 to 11% aluminum, up to about 7% copper, up to about 1% manganese, up to about 0.1% carbon, from about 0.15 to 1% silicon, and the balance substantially all iron, said magnet having a substantially single phase microstructure, being magnetically anisotropic and having a (BH)max value in the principal direction of at least 4.5 million.

JOHN R. HANSEN.

' REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,170,047 Donnohl Aug. 22, 1939 (Other references on following page) Number Country Date UNIIED STATES PAIENIS 1 446,894 Great Britain May 4, 1936 Numbezlgo Name ate 942 522,731 Great Britain July 26, 1940 2,293, Branburger Aug. 18, 1 2,295,082 Jonas Sept. 8, 1942 5 OTHER REFERENCES FOREIGN PATENTS 60gran and Steel, September 1944, pages 597 to Number Country Date 439,943 Great Britain Dec. 9, 1935 

1. A FERROUS ALLOY ADAPTED FOR USE IN PERMANENT MAGNETS CONTAINING: ABOUT 10 TO 20% NICKEL, ABOUT 16 TO 30% COBALT, ABOUT 6 TO 11% ALUMINUM, UP TO ABOUT 7% COPPER, UP TO ABOUT 1% MANGANESE, UP TO ABOUT 0.1% CARBON, FROM ABOUT 0.15% TO 1% SILICON, AND THE BALANCE SUBSTANTIALLY ALL IRON, SAID SILICON BEING PRESENT IN AMOUNT SUCH AS TO IMPART TO SAID ALLOY A SUBSTANTIALLY SINGLE PHASE MICROSTRUCTURE ON HEATING AT ABOUT 1600* TO 1700*F. AND COOLING THEREFROM. 